1. Field of the Invention
The present invention relates to keyswitches for use with keyboards having a matrix of row and column wires, and in particular to such a keyswitch which prevents the generation of false signals, but permits the circuit board for the keyboard to be manufactured without the necessity of soldering components thereto.
2. Description of the Prior Art
In keyboards comprising a plurality of keyswitches actuatable by means of depressable keys, each depressed key must be clearly electronically identifiable even if several keys are simultaneously actuated. In many keyboards, the keyswitches are respectively associated with intersection points of row wires and column wires of a wiring plate or circuit board having printed connectors disposed in a matrix, in order to maintain the number of exterior terminal connections as small as possible.
Upon depression of a key, a row wire is connected with the column wire disposed at the point of intersection beneath the key. In order to prevent the generation of false signals, so-called sneak paths, which may result upon the simultaneous actuation of several keys and which can cause erroneous identification of a non-depressed key, conventional keyboards employ decoupling diodes which are connected in series with the switching paths of the keyswitches. Such a keyboard is disclosed, for example, in "Selecting the Right Keyboard," Eikelberger, Machine Design, Nov. 12, 1981, pages 68-73. The decoupling diodes are connected to the circuit board of the keyboard, and require two solder points per keyswitch.
The elastomeric keyboards are also known in the art wherein a flexibile rubber-like sheet or mat having contact fields arranged thereon in a matrix grid corresponding to the arrangement of the keys on the keyboard are known in the art. The contact fields are linearly offset relative to each other and the sheet possesses elastically deformable, bubble-type raised portions. On the underside of the raised portion, contact plates are mounted which short circuit two adjacent contact points on the wiring plate or circuit board, which are respectively connected with a row wire and a column wire, when a key above the particular raised portion is depressed.
The use of elastomeric deformable keyboards makes possible the production of solder-free keyboards if decoupling diodes are not used. The use of decoupling diodes in combination with such keyboards, however, still requires soldering to the circuit board.